1. Field of the Invention
The present invention relates to a tin/indium alloy electroplating solution.
2. Description of the Related Art
The pollution of soil and subterranean water has recently become an issue, which pollution is caused by acid-rain elution of lead from tin/lead alloy used in waste home electronic and electric appliances. This is because tin/lead alloy is widely used in mounting electronic components. Therefore, the development of a mounting solder alloy or solder plating not containing lead is keenly desired. As a plating method not giving rise to such a problem, tin/indium alloy plating is now considered promising. The tin/indium alloy plating has heretofore been adopted as a low-melting plating, and in many of the conventional tin/indium alloy plating methods the indium content is 40 to 60 wt %. For example, in "Metal Surface Finishing (in Japanese)" Vol. 16, No. 6, pp. 246-250 (1965) there is disclosed an "Indium-tin alloy plating" solution as an indium alloy plating solution, in which the indium content is 50 wt % or so and sodium potassium tartrate is used as a chelating agent.
Also in "Metal Surface Finishing (in Japanese)" Vol. 15, No. 8, pp. 283-288 (1964) there is disclosed "Indium-tin alloy plating," in which, however, a cyanide and an alkali cyanide are used as essential components.
It is a principal object of the present invention to provide a cyanide-free tin/indium alloy electroplating solution capable of forming a tin/indium alloy plating film superior in smoothness in a wide electric current density range a n d capable of being put to practical use industrially.